Ficus bonsai dropping leaves and white powder

Question

So I bought a ficus microcarpa bonsai from the store 2 month ago and I noticed a problem since then, some leaves turn partially brown and fall while it's still wet not dry, some new growth also falls while still green, it falls at a rate of 1 leave/day.

The prime suspect is the white powder on the leaves, I tried washing it with distilled water but it didn't wash off.

I also checked the roots to see if the plant is root bound or has root rot but I don't think so as you can see in the picture.

So basically I have no idea what I'm doing wrong, this is my first bonsai, I would appreciate the help.

more info:

It's kept indoors with humidity between 40%-60% with a temperature range of 22-27 Celsius.

The main source of light is a CFL lamp 150 watts that is kept on for 8 hours a day, the lux reaching the leaves is 3000 lux with no hotspots.

I fertilized it twice a month with 1 gram of npk 20-20-20.

I water it with tap water when the top soil is dry.

Answer 1

The white powder is either pesticide residue or hard water residue from overhead watering. It does no harm and can be removed by rubbing the leaf with a cloth.

The root ball looks fine as the roots are firm with white new growth at the tips. There is no sign of the most common issue: over watering.

The leaf drop is well known with Ficus and new plants as they adjust to the light levels. Outdoor sunshine can be over 10,000 lux. One hopes the grower put the plant under shade cloth for a few months to get it adjusted to a light level of ~ 3000 to 5000 lux.

The plant cannot sustain dense foliage with one CFL lamp and is thinning out.

I recommend:

• do not fertilize for at least a few months. Fertilizer will encourage etiolation or stretching out of branches.
• water with filtered water. Tap water often contains chlorine or chloramine or both which can be detrimental in the long term
• thin the leaves and branches
• increase the light by moving next to a sunny window
• overwatering is the number one cause of indoor plant problems. Consider a wick system.